The origin of abnormal ferroelectric and unusual piezoelectricity in the polycrystalline CaCu 3 Ti 4 O 12 (CCTO) thin films deposited by RF-sputtering on Pt/Ti/SiO 2 /Si (100) substrates was explored. The CCTO thin films, deposited at room temperature followed by annealing at 600°C for 2 h in a conventional furnace, have a cubic structure with lattice parameter a = 7.379 ± 0.001 Å and without any secondary phases. No polarization loss up to 10 10 switching cycles, with a switched polarization ∆P of 30 µC/cm 2 measured at 400 kV/cm was evidenced. The piezoelectric coefficient investigated by piezoresponse force microscopy (PFM) was approximately 9.0 pm/V. This may be the very first example of exploring the origin of ferroelectric behaviour for a material that possesses space charge polarization with highly resistive grain boundaries in the polycrystalline state.
In this study, we investigated the structural, microstructural, magnetic and
cytotoxic properties of encapsulated ZnFe2O4 nanoparticles. The
nanoparticles were synthesized using the microwave-assisted hydrothermal
method and their surfaces were silanized and later encapsulated with
poly-2-hydroxyethyl methacrylate (PHEMA). Due to the compatibility of Zn2+
ions with a human body, ZnFe2O4 nanoparticles are preferable among all kinds
of ferrites for biomedical applications. Quantitative phase analysis
obtained by the Rietveld refinement reveals the formation of a single-phase
spinel cubic structure. Magnetic hysteresis loops measured at 2 and 300K
reveal a remanent magnetization of 4.427 emu/g and 1.002 emu/g,
respectively. Such behaviour was ascribed to change in the inversion degree
of the spinel structure. The experimental g-factor (g = 1.897) obtained
using electron paramagnetic resonance analysis can be attributed to the
microwave heating, which induces more surface-active oxygen species. In
addition, we demonstrated that the encapsulated ZnFe2O4 nanoparticles showed
an absence of cytotoxicity at concentrations of 1.0, 10 and 20 ?g/ml against
human embryonic kidney (HEK) cells since no significant changes in cell
morphology were observed. Hence, our results indicate the possibility to
explore the use of ZnFe2O4 nanoparticles encapsulated with PHEMA for
biomedical applications, such as cancer therapies.
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